Our long range goal remains performing experiments that help elucidate the regulation of alveolar turnover (formation and loss) in the hope this information might be therapeutically useful. Our past, and proposed, work are most relevant to bronchopulmonary dysplasia (BPD), a condition of very prematurely born infants in which arrested alveolarization is a key feature, and chronic obstructive pulmonary disease (COPD), in which alveolar destruction causes substantial morbidity and mortality. There is no remediation for the relentlessly progressive alveolar destruction of COPD, to which increasing evidence suggests women are more susceptible than men, and in whom the downhill course is more rapid. Key new findings since the last submission are: 1. Adult female estrogen receptor (ER)alpha and ERbeta k.o. mice have an alveolar phenotype - larger and fewer alveoli with less surface area than wildtype mice. 2. Ovariectomy in adult mice results, within 3 weeks, in a loss of 45% of alveoli and 13% of alveolar surface area. 3. Estrogen replacement, after alveolar loss has occurred, rescues the loss. 4. As proof of principle, we show in adult mice a) nasal instillation of microliter (fl) amounts of elastase in surfactant (SAM) resulted in severe diffuse emphysema thereby demonstrating diffuse alveolar delivery; b) a single nasal instillation of GAPDH RNAi in SAM (10- 15mu/l), compared with scrampled GAPDH RNAi, resulted in a 60-70% down-regulation, in a lung specific manner, of GAPDH protein from 24 h through 7 days; c) nasal instillation of retinoic acid (RA) in SAM caused a 4.6-fold increase in lung concentration of the mRNA of a marker protein in a lung specific manner; an equal concentration of RA given intraperitonealy caused a 1.8-fold increase in the marker mRNA in lung and an increase in brain and other organs. Our specific aims, using wild type and mutant mice, morphometric, and lung gene-expression profiling, are: 1. Determine the developmental time of onset of the ER alveolar phenotype; 2. Identify the ERs that mediate the ovariectomy-induced destruction of alveoli, and 3. Identify the upstream modulators that initiate the signal cascade required for estrogen-induced alveolar regeneration that follows ovariectomy. We think the new information generated since the first amended application, including the ability to alter expression of specific genes in a simple, noninvasive, lung specific manner, our extensive experience with morphometry, and now with lung gene profiling, will allow us to complete the proposed work.